This invention relates to fire resistant glazings, interlayers useful in such glazings, solutions useful in the production of these interlayers, additives useful in the preparation of said solutions, and methods of directing and/or stabilising the diversity and/or distribution of silicate structures in said solutions.
Fire resistant glazings comprising at least one interlayer comprising a silicate waterglass and at least two panes of glass are well known. When these laminates are exposed to a fire, the interlayer intumesces and expands to form a foam. The foam helps to maintain the integrity of the glazing thereby restricting the spread of a fire and also provides a thermally insulating layer which acts as a barrier to infra-red radiation. These glazings can meet the requirements of most applicable building regulations and are widely used in architecture and building.
In order to be useful, the interlayers must be optically clear and retain that clarity throughout the lifetime of the glazing. They must also provide the required degree of fire resistance. Interlayers which comprise a higher proportion of silica impart a higher degree of fire resistance to the glazing but are more difficult to manufacture as optically clear materials.
The interlayers may be manufactured using a variety of processes. The most widely used process involves pouring a silicate waterglass solution onto the surface of a glass pane and drying that solution under carefully controlled conditions. Such processes are described for example in GB 1518958, GB 2199535, U.S. Pat. No. 4,451,312, U.S. Pat. No. 4,626,301 and U.S. Pat. No. 5,766,770. A variant upon this process in which a silicate solution is dried upon a flat surface to form a film which can be separated from that surface and used as an interlayer is described in WO 01/70495. EP 620781 describes a process in which a silicate solution is poured into the space between two opposed glass panes and allowed to self cure to form a fire resistant glazing.
Whatever the method by which they are produced these silicate based interlayers and the waterglass solutions from which they are produced comprise a plurality of silicate anions. The precise composition of the interlayers and thereby their properties, varies with the conditions under which they are produced. The nature of silicate structures in solution may be thought of as silicon surrounded by oxygen in an almost regular tetrahedron. Pure silicic acid, Si(OH)4, however, does not exist in solution. Condensation reactions occur between such units giving rise to silioxane (Si—O—Si) bridges. The silicon-oxygen tetrahedra may therefore share a corner which, in turn, gives rise to a wide variety of silicate structures in solution.
In order to describe such structures it is convenient to adopt the ‘Q’ nomenclature used by Engelhardt et al. (G. Engelhardt and O. Rademacher, J. Mol. Liquids, 1984, 27, 125). The “Q-unit” (for quadrifunctional) represents a SiO4 group with the number of other Q-units directly attached to the one under consideration, indicated by a superscript. Taking the example of the condensation reaction mentioned above, the silicic acid species would be denoted as a Q0 species as the silicon has no siloxane bridges to any other silicon atoms. The dimer formed from the condensation reaction however, would be denoted as Q12 as each silicon atom is bonded to one other via a siloxane bridge. Additional condensation reactions give rise to a wide variety of silicate structures, groups of which may be assigned a Q number and hence easily referred to.
A need exists to improve the mechanical properties of silicate interlayers particularly in the elastomeric range of silicate materials. Currently, silicate interlayers are brittle and therefore difficult to handle and cannot be manipulated. Accordingly, a need exists for a silicate solution that has the potential to dry or cure to form a flexible film. It would also be beneficial to control to varying degrees the structural homogeneity of silicate interlayers, thereby controlling cohesion and water distribution throughout the interlayers.